The very biggest Question is How are planets formed?


Planets are thought to have formed the solar nebula.  The solar nebula is a disc-shaped cloud of gas and dust left over from the Sun's formation. The currently accepted method by which the planets formed is accretion, in which the planets began as dust grains in orbit around the central protostar. As clouds collapsed they started rotating in the same direction. Then, they started through direct contact, material began to stick together creating larger and larger clumps, these clumps formed up to 200 meters in diameter, which in turn collided to form larger bodies’ planetesimals (the beginnings of a planet) of ~10 kilometers (km) in size. These gradually increased through further collisions, growing at the rate of centimeters per year over the course of the next few million years. After millions of year and many collisions, a planetary system begins to reach maturity.
Our solar system began forming about 4.6 billion years ago within a concentration of interstellar dust and hydrogen gas called a molecular cloud. The cloud contracted under its own gravity and our proto-Sun formed in the hot dense center. The remainder of the cloud formed a swirling disk called the solar nebula.
Within the solar nebula, scientists believe that dust and ice particles embedded in the gas moved, occasionally colliding and clumping together. Through this process, called "accretion," these microscopic particles formed larger bodies that eventually became planetesimals with sizes up to a few kilometers across. In the inner, hotter part of the solar nebula, planetesimals were composed mostly of silicates and metals. In the outer, cooler portion of the nebula, water ice was the dominant component.
The Sun is a star and the largest object in the Solar System, where it lies in the middle of the galaxy and is 92.95 million miles away from the earth. The sun is orbited by matter including: planets, comets, asteroids, meteoroids, and dust. The sun is a major and important source of energy for life on earth (giving a photosynthesis to plants and other life forms) and drives the earth's climate and weather.

Containing 99.8% more of the total mass of the Solar System (since Jupiter contains the rest). Currently, the mass of the sun is about 70% hydrogen, 28% helium by mass, and less than 2% of other metals. It slowly changes over time as the sun converts hydrogen to helium in its core. Producing around 3.86e33 megawatts by nuclear fusions reactions, it's considered to be the sun's energy output. Traveling out toward the surface, the energy is continuously absorbed and re-emitted lower temperatures, therefore by the time it reaches the surface, the light is primarily visible.

The Sun is roughly middle aged and has not changed dramatically for over four billion years, and will remain fairly stable for more than another five billion years. However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes and become a red giant.

Harboring Energy
Solar energy is radiant light and heat from the Sun harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture and artificial photosynthesis.

It is an important source of renewable energy and its technologies are broadly characterized as either passive solar or active solar depending on the way they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power and solar water heating to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.